Ventilation depends upon the ability of the respiratory pump to move air in and out of the gas exchanging portion of the lungs. The dome-shaped diaphragm is the chief muscle of inspiration and the most powerful of the respiratory muscles [1-3]. The other main muscles of inspiration are the scalenes, external intercostals, and sternomastoids. The muscles of expiration are the internal intercostals and the muscles of the abdominal wall (including the rectus abdominus, internal and external obliques, and transversus abdominus).

In addition to its role in the respiratory pump, the diaphragm also serves as a mechanical barrier between the abdominal and thoracic cavities and maintains the pressure gradient between the cavities.

The diaphragm has two components: the non-contractile central tendon that separates the right and left sides and extends to the dome of each hemidiaphragm and the contracting muscle fibers [1-3]. The diaphragmatic muscle fibers radiate centrifugally and insert peripherally onto the inner surface of the lower six ribs laterally, the costal cartilages and sternum anteriorly, and the arcuate ligaments that extend from the upper lumbar vertebrae to the 12th ribs posteriorly [4]. The crura are posterior muscle bundles that run from the medial central tendon to the upper lumbar vertebral bodies posteriorly (L1 to L3 on the right, and L1 to L2 on the left).

The left and right sides of diaphragm are innervated by the ipsilateral phrenic nerves, which derive from cervical nerve roots three, four, and five [4]. Each nerve divides into four trunks that innervate the anterolateral, posterolateral, sternal, and crural portions of the diaphragm on that side.

To continue reading this article, you must log in with your personal, hospital,
or group practice subscription. For more information or to purchase a personal subscription, click below on
the option that best describes you: